Cellulosic product



Patented Feb. 22, 1944 CELLULOSIC PRODUCT Richard Ericson, Chicago, Ill., assignor to United States Gypsum Company, Chicago, 111., a corporation of Illinois No Drawing.

Application November 18, 1940,

Serial No. 866,139

11 Claims.

The present invention relates to an improved cellulosic product, preferably in sheet form, particularly useful where a hard, dense'and waterresistant product is desired. More specifically, it relates to a consolidated fibrous product having a-high modulus of rupture and considerable resistance to moisture.

One of the objects of the present invention is to provide a method for the production of a compressed or consolidated fibrous product which may, for example, be made from wood fiber and which, after consolidation, is partly impregnated with a material capable of being hardened, as by oxidation and/or polymerization, and which is subjected to a certain specific method of heat treatment which favors the oxidation and polymerization so as to yield a particularly desirable product.

While it has already been proposed to impregnate fibrous materials with drying oils and the like and then to bake them, either too little oil has been used to penetrate clear to the core of the material or, if enough has been used, the conditions of oxidation were such as to produce a skin at or near the surface of the material, which interfered with the proper hardeningthat is, oxidation and polymerization-of the material in the interior'of the product. It has been contended by some prior art workers that the use of more than 50% of the amount of 011 required for complete saturation was undesirable and would not yield a commercia1 product of satisfactory properties. However, by practicing the process of the present invention, it is possible to employ more than 50% of the amount of impregnant which would be required for complete saturation and still obtain a commercially desirable, highly water-resistant product. Such a product, while not completely saturated-that is to say, while not having absorbed all of the impregnant that it would be possible to introduce, is nevertheless impregnated clear to the interior or core thereof, so that there will be very little tendency for expansion upon absorption of moisture.

Attempts have been made in the past to obtain this type of impregnation of, for example, a heat and pressure consolidated cellulosic material made from wood fiber, by dissolving,- thinning out or diluting the impregnating material with a solvent which was volatile and hence subsequently could be removed. While it was found that the core of the material could readily be reached in this manner, such a product was not commercially feasible because of th inordinately high cost occasioned by the use of the solvent, which in most cases was diiiicult to recover, coupled with the fact that the use of such solvents represented a great fire and explosion hazard. When it is considered that the material which forms the preferred subject matter of the present invention is a building material which must be sold at a relatively low price, it will be-seli evident that expensive impregnating methods could only be applied thereto at a cost which would make it unattractive to the purchaser.

A further object of the present invention therefore relates to a means by which a heat and pressure consoiidated cellulosic product may be impregnated clear through to the center so as to produce, icr example, boards having high water resistance and strength despite the fact that more than of the amount of impregnant required for complete saturation has been employed,

A further object of the invention is to accomplish the aforesaid results without the necessity of using volatile solvents which require subsequent removal.

A stil further object of the invention relates to the methods by which the bleedin or migratlon of the impregnating material to th surface of the product during the hardening step are prevented.

While the present invention is applicable to the treatment of a considerable variety of fibrous materials and is therefore not to be limited to the precise examples given, it will be described in connection with the manufacture of what is commercially known as hardboard, which is a heat consolidated cellulosic product usually made from lignocellulosie materials such as wood, wood fiber, and the like, which has been compressed and heated so as to activate the bonding properties of the incrustants commonly found in such lignocellulosic raw materials.

The precise method for making the hardboard, which it is the object of the present invention further to improve by impregnation, is'of comparatively little concern so far as the invention is concerned. The board may be made by either the wet or the dry method, and, in general, methods of manufacturing such hardboard are already well established and thoroughly understood by the workers in this art.

The impregnating materials employed in the present invention are of an oleaginous nature and are characterized by the fact that they may be rendered substantially insoluble in organic solvents by the combined efiect 01 heat and oxidation, probably also coupled with polymerization. Stated in another way, these materials may be said to possess the properties generally attributed to the drying oils, which, as is well known, are capable of absorbing oxygen, thereby becoming oxidized, and are also capable of becoming polymerized simultaneously with or subsequently to the oxidation, so as to produce relatively tough water-resistant bodies which, while they lend additional strength to the product, also render it much more water resistant.

In accordance with one embodiment of the present invention, some of this type of material may be incorporated with the hardboard prior to the impregnating step. For example, a suspension of suitably comminuted wood fibers may be placed in water, to which suspension there may be added an emulsion of the drying oil material or its equivalent, this emulsion then being broken in a well-known manner, as by the addition of precipitating chemicals, such as paper makers alum and the like, so as to effect precipitation of this oleaginous material upon the fibers, whereafter the suspension may be formed into a coherent mat, as for instance on a Fourdrinier wire or other board-forming device, to produce a thick wet lap which may then be consolidated and dried. One advantageous method of accomplishing this is to dry the wet lap without compression and then to store it for possibly several days to permit an initial oxidation of the oleaginous material, following which the dry boards thus obtained may be consolidated under heat and pressure, as for example by being compressed at, let us say, 1500 pounds per square inch pressure at a temperature between 350 F. and 500 F. The board thus obtained may then be employed for carrying out the impregnating and baking steps more particularly hereinbelow described. Alternatively, the board may be made without any initial oil in it and then employed in the impregnating step.

While the various drying oilssuch as linseed oil, tung oil, soybean oil, and their equivalentsare satisfactory for carrying out the present invention, it has been found advantageous to produce a mixture of natural as well as synthetic materials so as to produce the most desirable results, but obviously the invention is not to be limited thereby.

A good formula for carrying out the invention is the following: 42 parts of polymerized dioleflns having an iodine number of about 200 and containing about 92% of solids dissolved in a liquid of similar nature which is capable of turning into a solid when heated, about 35 parts of the glyceride of a highly unsaturated fatty acid of a marine oil either in polymerized or unpolymerized form and having an iodine number of about 170. about 25 parts of raw soybean oil, and about 0.1 part of zinc as zine naphthenate drier and about 0.32 part of lead as lead naphthenate drier or equivalent catalytic material which assists in the oxidation and polymerization of the aforementioned mixture of products. The lead may be replaced by an equivalent amount of zinc, with comparable results.

It will be obvious that in the foregoing example linseed oil may be substituted for the unsaturated glyceride and also that an introfier may be employed to assist in lowering the apparent viscosity of'the mixture, to assist in its penetration into the board. A substance which lowers the surface tension of the material is commonly known as an introfier.

In carrying out the impregnation, the above mentioned mixture or its equivalent is heated to a temperature of about 250 F., although higher or lower temperatures may be used. The fibrous blanks or boards made in any suitable manner, as for example by the method above indicated, are immersed in this impregnating bath for a time sufficient to absorb and retain somewhat over half the amount of impregnating material that they would absorb if the impregnation were carried on long enough to cause complete impregnation. The time required to effect this has to be determined by experiment and will vary with the various types of board, and particularly the density thereof. It is advantageous to use board which still contains hygroscopic moisture, as the latter will be turned into steam as a result of the temperature of impregnation and the escape thereof will make room for the penetration of the impregnant. It is believed that such moisture acts in part as an introfier for the impregnating material. The time of impregnation will naturally vary with a number of factors. For instance, as an illustration, a consolidated fibrous board /8" thick having a density of approximately 66 pounds per cubic foot will have an oil penetration completely to the center when impregnated with the aforementioned composition for about 45 minutes at 250 F. Thicker boards will require longer time. It will be found that from about 50% to 75% of complete saturation will be sufficiently properly to impregnate such a board through to the center of the core, the usual range lying somewhere between 50% and 60% of complete saturation. If oil has already been incorporated with the board prior to impregnation, that is to be taken into consideration in this calculation.

What is meant by 50% to 75% of total saturation is the following: If such a board were capable of absorbing, say, 25% of the weight thereof when the impregnation is carried out until no further increase in weight is obtained, then about from 12.5% to 15% of impregnant should be added to the board, based upon the original weight thereof. For that reason, it is best to make an experiment to determine the total amount of impregnant which the board is capable of absorbing, as for example by extending the impregnating period for a long time and then to adjust the impregnating conditions, when working in accordance with the present invention, to the point where the board will absorb a little more than half the total amount of oil that would be required for complete or total impregnation or saturation.

After the board has been kept immersed in the heated impregnating bath for a length of time to cause absorption of the desired amount of impregnant, it is removed, and any of the impregnant remaining on the surface thereof is removed therefrom, as for example by means of an oilresisting composition roll, wiper, or similar means.

It may be desirable to stack the board flat and let them lie for some time to insure the complete and uniform dispersion of the impregnani therein.

To provide a uniform means for distributing the impregnating compound, it is desirable to apply a thin coat of the impregnating compound to the edges of the boards first to permit same to dry slightly and thus form a seal. During impregnation the impregnating material can only reach the interior through both large surfaces and is prevented from striking in along the edges, which because of their fuzzy and open structure permit more rapid impregnation along the margins of the board. Boards containing more impre fact, heating them at a constant high temperavnant alongthe margins of their edges are likely ture will cause a bleeding of the impregnant back to the surfaces of the boards, so that the surfaces will be discolored and rough and thus the utility of the boards will be decreased. Further more, this migration forms a'skin which prevents the proper oxidation, polymerization and hardening of the impregnant which is further down toward'the center or core of the boards. It is believed that by keeping the initial baking temperature rather low, the material is first oxidized or partially polymerized to such a point that on subsequent heating it will not reach the surface, so that it can then withstand the higher temperatures required for its complete hardening.

However, the exact nature of this phenomenon is not understood at the present time.

A further advantageous manner of carrying out the invention is to place the impregnated fibrous blank, preferably after storing as indicated, into an air drier in which it is first maintained at a temperature only slightly above the boiling point of water-let us say, for example, at 225 F. This low temperature baking or heating should be carried out for a period of about six hours. Thereafter the temperature should be raised slowly during a period of about two hours until it lies between 285 F. and 325 F., within which range it should be maintained for a period of, say, twelve to sixteen hours. A very advantageous cycle is about six hours at 225 F.,, two hours to raise the temperature from 225 F. to the upper range of between 285 F. and 325 F., and then to maintain it within the upper range for about sixteen hours, thus making a total twenty-four-hour period of baking.

Various modifications of the baking cycle and various methods of baking, such as with pressure or by using steam coils, lamps, etc., can be used and still be within the scope of this invention.

At the end of the baking period the boards are removed from the oven and as soon as possible placed in surroundings which will both 0001 them and humidify them. Despite the fact that the boards of the present invention are water resistant to a marked degree, they will nevertheless absorb some atmospheric moisture, which were it not deliberately introduced before the boards had cooled-would cause them to warp. However, by proper humidification, they will be at equilibrium with the ordinary atmosphere and hence will show no tendency to expand or contract when used by the ultimate purchaser.

The boards of the present invention may find utilization in the building industry or may be used for concrete forms, shipping cases, signboards, and the like; and they also may be readily painted or otherwise decorated with a minimum expenditure by coating materials, as they have comparatively little suction. In other words, they would require no preliminary filling before being painted or varnished.

It has been found that when carrying out the baking cycle as hereinabove indicated, there is a marked increase in the modulus of rupture of the boards which is quite diiferent from that which would be obtained if the boards were immediately heated to a high temperature. solely as an example of this difference, it may be stated that two boards impregnated with the same amount of impregnant of the same kind were tested side by side. One of them was baked six hour at 225 F. and then for four hours at 285 E, which increased its modulus of rupture from 7945pmmdsper square inch to 9920 pounds. The

same board, however, which was first baked for six hours at 225 F. and then baked for fourteen hours at 285 F., had its modulus of rupture increased up to 11,640 pounds per square inch.-

Another board, which had been impregnated and baked for six hours at 225 F., had a modulus of rupture of only 8495 pounds per square inch. The first mentioned board had a water absorption in 24 hours of 14%, while the second board had one of only 7.7%, and the last mentioned board had one as high as 22.5%. It will thus be seen, for example, that baking for six hours at 225 F.followed by baking for fourteen hours at 285 F. gives a very much improved results.

The exact instrumentalities employed for carrying out the present invention are well known, and the impregnation of the boards may be carried out either horizontally or vertically. The baking ovens are preferably of a kind upon which the board is gradually propelled on rollers through a long drying oven, the first portion of which is maintained at the lower temperature and the other portion at the higher temperature.

However, these are mere operating details which are not limitations in any sense upon the present invention, for which the inventor claims:

1. The process of producing high strength water-resistant hardboard which comprises impregnating hardboard with from 50 to 75% of its saturating capacity of a drying-oil material and then heating the board first for a period of about six hours at slightly above the boiling point of water and thereafter heating it at about 285 F. to 300 F. for a period of twelve to sixteen hours.

2. The process of producing high-strength water-resistant compressed celiulosic products which comprises impregnating a compressed cellulosic product with from 50% to 75% of its saturating capacity with a heat-hardenable drying oil material, stacking the thus hot impregnated cellulosic products in superimposed contacting relationship to permit penetration of said material into the center of the product and to effect equalization of its distribution therein, thereupon subjecting the thus treated product to a temperature near the boiling point of water for a time sufficient to cause the escape of moisture therefrom, and thereafter baking the thus treated product at a higher temperature but not substantially exceeding 325 F. to effect the hardening of the oily material with which it is impregnated.

3. The process of producing a fiber board of improved strength and water resistance, which comprises providing in the interstices thereof an an oxidizable drying oil material, and heating the board containing said material first at a relatively low temperature near the boiling point of water to permit initial oxidation thereof, and then heating to a higher temperature, not substantially exceeding 325 F. to oxidize and harden the said drying oil material.

4. The process of improving the strength and water-resistance of the heat-and-pressure consoiidated iibrcusvegetable product which comprises impregnating said product with from between 50% to 75% of what the said product impregnated product at a temperature approximating the boiling point of water for a time sumcient to remove the moisture therefrom, but without exerting any extensive hardening effect on said material, and to cause penetration of said material to the centerof the product, and thereafter heating the thus impregnated and dried product at a temperature well above the boiling point of water, but not substantially exceeding 325' I". for a time sufficient to harden the drying oil material within the fibers of the product.

5. The process of improving the strength and water resistance of a heat-and-pressure-consolidated hardboard comprising saturating said board with an oil characterized by its properties of being rendered substantially insoluble in organic solvents by the combined effects of heat and oxidation, to the extent of from 50% to 75% of what said board could completely take up, said impregnation being effected at a temperature above the boiling point of water but no greater than 300 F., permitting said impregnated boards to remain piled in a stack to enhance the penetration of the oil into the center of the board, heating the thus impregnated board to remove any water therefrom, and then further heating it to from 285 F. to 325 F. to harden and polymerize said oil.

6. A heat-and-pressure-consolidated vegetable fibrous material of high strength and high water resistance containing between 50 and 75% of a heat-hardened oxidized oil, characterized by its properties of being rendered substantially insoluble in organic solvents by the combined effect of heat and oxidation, said percentage being based upon the total amount of such substance which said material could absorb.

"I. A heat-and-pressure-consolidated vegetable fibrous material of improved strength and water resistance comprising a dense vegetable fiber base, 50 to 75% of the saturable volume of which contains a heat-hardened oxidized oil. characterized by its properties of being rendered substantially insoluble in organic solvents by the combined effect of heat and oxidation, the surfaces of said consolidated material being substantially free from discolored areas resulting from the bleeding of said oil to the surface of said material.

ass'aau acterlsedbyitspropertiesofbeingrenderedsub-' stantially insoluble in organic solvents by the combined eifect of heat and oxidation. the modulus of rupture of said sheetbeing notiessthan 10,000 pounds/square inch and the amount of water absorbed at 1 in 24 hours not over 12% y weisht.

9. An improved hardboard sheet of high strength and water resistance comprising a heatand-pressure-consolidated fiber base, 50 to 15% of the interstitial voids thereof containing a heat-hardened oxidized oil. characterized by its properties of being rendered substantially insolu. ble in organic solvents by the combined effect of heat and oxidation extending to the center of said sheethboth surfaces of said sheet being smooth and substantially free from blisters and blemishes due to bleeding of the oil to the surface.

10. The process of producing high strength water-resistant hardboard which comprises impregnating hardboard with from 50% to ofhours.

11. The process of producing high strength water-resistant hardboard which comprises impregnating hardboard with from 50% to 75% of its saturating capacity of an impregnant containing about 42 parts by weight of a polymerized diolefine having an iodine number of about 200 and containing about 92% of solids dissolved in a liquid of similar nature as the dioleflne which liquid is capable of becoming solid when heated, about 35 parts of the glyceride of a highly unsaturated fatty acid and having an iodine number of about and about 25 parts of soybean oil, and small amounts of driers, heating the impregnated board at about 250 F., for a period of about six hours, and then increasing the temperature to within a ranse of between 285 F. and 325 F., and continuing said heating at the higher temperature for from 12 to 16 hours.

RICHARD ERICSON. 

